The present invention relates to a method of, and system for, describing a geographical area to a communications network in order to restrict the transmission of data to that area. The present invention has particular, but not exclusive, application for relaying traffic information to vehicles in a predetermined geographical areas.
In many countries there already exist information centres which gather and retain information about road traffic flow behaviour for example that traffic is flowing freely through a junction, that traffic lights have failed causing a traffic jam and that there has been an accident and traffic has been held up. Such information is regularly broadcast over public radio systems so that anyone having a suitably tuned receiver hears the information irrespective of whether they have any interest in it.
Road traffic information and vehicle navigation systems are currently under development in different countries of the world. A European wide project called SOCRATES envisages communicating information to a computer carried in a vehicle by radio using the GSM digital cellular telephone network. As the information to be transmitted may be relevant to a relatively small geographical area only it is pointless for an entire network to broadcast such information nationwide.
Although the locations of most cellular telephone or cellular radio base stations are fixed, operators frequently want to keep such information confidential. Additionally depending on the current level of telephone or radio traffic through a base station and/or the serviceability of the base station, the network operator may want to reconfigure his network by altering the size and/or shape of the coverage area of one or more base stations for example by varying the transmitter output power and/or modifying the antenna arrangement to make transmissions directional rather than omnidirectional. In view of this a traffic centre which is operated independently of a cellular telephone or radio network cannot for example instruct a cellular network operator which particular base stations of the network should carry traffic information relating to an incident.